This invention relates to an improvement in the belt structure for a pneumatic tire, in particularly for high-speed tires.
Typically, the belt of a tire is subjected to many different conditions while being used on a motor vehicle. The tire goes through turns, curves, adverse road conditions and is expected to respond to these many conditions. The belt structure during such condition is required to be flexible and resilient with the tire as well as maintain structural rigidity when the tire is being driven upon. The belt structure is most severely stressed when the tire travels around turns and curves. During this time the cords in the belt are placed in tension. The edge of the belt after frequent exposure to stress/strain cycles could potentially lose some of its structural integrity.
An improvement in the belt structure would be to reduce the stress and strain levels that the belt structure is subjected to during normal driving conditions.
A typical belt structure is made of one or more plies of material arranged in the radial planes of the tire. Ply material used in the belt has been either fabric (i.e. fiberglass, aramid) or metallic (i.e. steel) or composite material (fiberglass-aramid, aramid-nylon, etc.). Several strands of this material typically is bundled together to form twisted cords. The cords are then imbedded in a elastomeric type substance before being used in the belt structure. The elastomeric substance used for this process is usually rubber or one of its by-product. During belt manufacturing these coated twist cords are disposed circumferentially around the carcass of the tire. The belt structure then is imbedded into the carcass and becomes a part thereof.
The belt structure that seems to function better for the present invention comprises cords that vary from 6 ends/inch to 35 ends/inch depending on cord gauge being used. The bias angle for the belt structure cords positioned centrally on the belt ply varies from 15 degrees to 40 degrees.
The present invention in the belt structure minimizes stress loading that the belt structure normally encounters by folding the belt on at least one of its edges. This reduction in stress occurs because the twist cords when folded loosens; and thus relieves stress that exists as a result of the twists in the cords.